Progressive multifocal lenses typically comprise a far-vision region having one refractive power, a near-vision region having a different refractive power, and an intermediate progressive region.
In a common method for producing progressive multifocal lenses, a semi-finished lens blank having suitable optical characteristics is selected based on a prescription. Typically the semi-finished progressive lens blank comprises a front progressive multifocal surface and a back spherical surface. The back surface of the semi-finished lens blank is then machined and polished to match the prescription. Unfortunately, current semi-finished progressive lens blanks are relatively expensive.
An alternative method for producing multifocal progressive lenses uses less expensive single vision semi-finished lens blanks having a front spherical surface and a back spherical surface. Based on the prescription, a single vision semi-finished lens blank having a suitable optical power is selected. A progressive surface design is then computed in accordance with the prescription, and the back surface of the lens blank is machined and polished to produce the desired progressive surface. Although less expensive, this method for producing multifocal progressive lenses is relatively time consuming, partly due to the computational complexity of computing the progressive surface for each prescription.